Corneal infections and ulceration are significant causes of visual impairment and blindness worldwide. Filamentous fungi of the Aspergillus and Fusarium genera are a leading cause of these corneal infections, accounting for upwards of 50% of microbial keratitis cases in developing countries, where warm climates and a high volume of agricultural labor predisposes to spore (conidia) exposure and ocular trauma. They are also a concern in the United States due to increasing contact lens use, use of topical corticosteroids and ocular surgery. An outbreak of Fusarium keratitis associated with a particular lens care product in 2005-2006 was investigated by the CDC and resulted in recall of the lens solution. The ubiquitous presence of fungal conidia in the environment means that these infections are an ongoing concern. Current anti-fungal therapies are limited and plagued by severe side-effects and increasing resistance of many fungal species. Thus, there is a need for greater understanding of fungal infection pathophysiology and more effective therapeutic tools. Our lab has a well-established murine model of fungal keratitis in which we have identified the importance of neutrophils (PMNs) in anti-fungal defense, in part due to reactive oxygen species (ROS) production and nutrient iron chelation. Using this model and isolated neutrophils, proposed studies seek to broaden the role of PMNs in anti-fungal immunity by testing the hypothesis that neutrophil S100A8 and S100A9 (dimer: calprotectin) is necessary for optimal fungal control through zinc chelation and subsequent inhibition of fungal antioxidant defenses (Aim 1). The second major goal of the study will be to investigate the formation of neutrophil extracellular traps (NETs) in the cornea during fungal keratitis and use chemical inhibitors and knock-out mice to determine the necessity of NETs, and NET-mediated calprotectin release, in anti-fungal immunity (Aim 2). NETs are potentially damaging to host tissue and we will determine whether these structures lead to unnecessary ocular inflammation and damage, and whether blocking NET release represents a potential therapeutic strategy. At the conclusion of these studies we will better understand how neutrophils control fungal infection and how we can co-opt strategies such as zinc sequestration for therapeutic purposes. We will also determine whether some neutrophil defenses contribute to corneal opacification and vision loss which will lead to more effective management of fungal keratitis.